Hedgehog-signalling in papillary fibroblasts is essential for hair follicle regeneration during wound healing

Inhibiting mechanotransduction prevents scarring and yields regeneration in a large animal model

Modulating mechanotransduction by inhibiting yes-associated protein (YAP) in mice yields wound regeneration without scarring. However, rodents are loose-skinned and fail to recapitulate key aspects of human wound repair. We sought to elucidate the effects of YAP inhibition in red Duroc pig wounds, the most human-like model of scarring. We show that one-time treatment with verteporfin, a YAP inhibitor, immediately after wounding is sufficient to prevent scarring and to drive wound regeneration in pigs. By performing single-cell RNA sequencing (scRNA-seq) on porcine wounds in conjunction with spatial proteomic analysis, we found perturbations in fibroblast dynamics with verteporfin treatment and the presence of putative pro-regenerative/profibrotic fibroblasts enriched in regenerating/scarring pig wounds, respectively. We also identified differences in enriched myeloid cell subpopulations after treatment and linked this observation to increased elaboration of interleukin-33 (IL-33) in regenerating wounds. Finally, we validated our findings in a xenograft wound model containing human neonatal foreskin engrafted onto nude mice and used scRNA-seq of human wound cells to draw parallels with fibroblast subpopulation dynamics in porcine wounds. Collectively, our findings provide support for the clinical translation of local mechanotransduction inhibitors to prevent human skin scarring, and they clarify a YAP/IL-33 signaling axis in large animal wound regeneration.

Assembly of Recombinant Proteins into β-Sheet Fibrillating Peptide-Driven Supramolecular Hydrogels for Enhanced Diabetic Wound Healing

Supramolecular hydrogels offer a noncovalent binding platform that preserves the bioactivity of structural molecules while enhancing their stability, particularly in the context of diabetic wound repair. In this study, we developed protein-peptide-based supramolecular hydrogels by assembling β-sheet fibrillizing peptides (designated Q11) with β-tail fused recombinant proteins. The Q11 peptides have the ability to drive the gradated assembly of N- or C-terminal β-sheet structure (β-tail) fused recombinant proteins. We first investigated the assembly properties of Q11 and assessed its stability under varying pH and temperature conditions by combining Q11 with two β-tail fused fluorescent proteins. The results showed that Q11 enhanced the tolerance of the fluorescent proteins to changes in pH and temperature. Building upon these findings, we designed collagen-like proteins and Sonic Hedgehog-fused recombinant proteins (CLP-Shh) that could be assembled with Q11 to form peptide-protein supramolecular hydrogels. These hydrogels demonstrated the ability to improve cell viability and migration and upregulate key markers of cell growth. Further in vivo studies revealed that the Q11-driven supramolecular hydrogel effectively enhances diabetic wound healing and epidermal regeneration by promoting the expression of epidermal-related proteins and immune factors. This study highlights the potential of supramolecular hydrogels for clinical applications and their promise in the development of biofunctional hydrogels for therapeutic use.

Dermal β-Catenin Is Required for Hedgehog-Driven Hair Follicle Neogenesis

Hair follicle neogenesis (HFN) occurs after large skin excisions in mice, serving as a rare regenerative model in mammalian wound healing. Wound healing typically results in fibrosis in mice and humans. We previously showed that small skin excisions in mice result in scarring devoid of HFN, displaying features of nonregenerative healing, and hedgehog (Hh) activation in the dermis of such wounds can induce HFN. In this study, we sought to verify the role of dermal Wnt/β-catenin signaling in HFN because this pathway is essential for hair follicle development but is also paradoxically well-characterized in fibrosis of adult wounds. By deletion of β-catenin in large wound myofibroblasts, we show that Wnt/β-catenin signaling is required for endogenous mechanisms of HFN. By utilizing a combined mouse model that simultaneously induces deletion of β-catenin and constitutive activation of Smoothened in myofibroblasts, we also found that β-catenin is required for Hh-driven dermal papilla formation. Transcriptome analysis confirms that Wnt/β-catenin and Hh pathways are activated in dermal papilla cells. Our results indicate that Wnt-active fibrotic status may also create a permissive state for the regenerative function of Hh, suggesting that activation of both Wnt and Hh pathways in skin wound fibroblasts must be ensured in future strategies to promote HFN.

Programmed BRD9 Degradation and Hedgehog Signaling Activation via Silk-Based Core-Shell Microneedles Promote Diabetic Wound Healing

Wound healing impairment in diabetes mellitus is associated with an excessive inflammatory response and defective regeneration capability with suppressed Hedgehog (Hh) signaling. The bromodomain protein BRD9, a subunit of the non-canonical BAF chromatin-remodeling complex, is critical for macrophage inflammatory response. However, whether the epigenetic drug BRD9 degrader can attenuate the sustained inflammatory state of wounds in diabetes remains unclear. Without a bona fide immune microenvironment, Hh signaling activation fails to effectively rescue the suppressed proliferative ability of dermal fibroblasts and the vascularization of endothelial cells. Therefore, a silk-based core-shell microneedle (MN) patch is proposed to dynamically modulate the wound immune microenvironment and the regeneration process. Specifically, the BRD9 degrader released from the shell of the MNs mitigated the excessive inflammatory response in the early phase. Subsequently, the positively charged Hh signaling agonist is released from the negatively charged core of the silk fibroin nanofibers and promotes the phase transition from inflammation to regeneration, including re-epithelialization, collagen deposition, and angiogenesis. These findings suggest that the programmed silk-based core-shell MN patch is an ideal therapeutic strategy for effective skin regeneration in diabetic wounds.

Fibroblast-Mediated Macrophage Recruitment Supports Acute Wound Healing

Epithelial and immune cells have long been appreciated for their contribution to the early immune response after injury; however, much less is known about the role of mesenchymal cells. Using single-nuclei RNA sequencing, we defined changes in gene expression associated with inflammation 1 day after wounding in mouse skin. Compared with those in keratinocytes and myeloid cells, we detected enriched expression of proinflammatory genes in fibroblasts associated with deeper layers of the skin. In particular, SCA1+ fibroblasts were enriched for numerous chemokines, including CCL2, CCL7, and IL-33, compared with SCA1- fibroblasts. Genetic deletion of Ccl2 in fibroblasts resulted in fewer wound-bed macrophages and monocytes during injury-induced inflammation, with reduced revascularization and re-epithelialization during the proliferation phase of healing. These findings highlight the important contribution of fibroblast-derived factors to injury-induced inflammation and the impact of immune cell dysregulation on subsequent tissue repair.

Hormonal interventions in skin wounds - a mini review

The ability to heal from wounds is perhaps the most important biological function that ensures our survival and perpetuation. Cutaneous wound healing typically consists of four characteristic stages, namely hemostasis, inflammation, proliferation, and remodeling, which are carefully carried out by coordinated actions of various cells, cytokines, and hormones. Incoordination of these steps may impede complete and efficient reconstruction and functional recovery of wounds or even lead to worsened outcomes. Hormones, as powerful modulators of organ functions, participate in multiple steps of the wound healing process and play a pivotal role by choreographing the complex interplay of cellular and molecular events. Leveraging the regulatory effects of hormones to enhance the healing process, hormonal therapy has emerged as a promising approach in the clinical treatment of wounds. Current research has focused on determination of the optimal dosages, delivery methods, and combinations of hormonal therapies to maximize their therapeutic benefits while minimizing potential side effects. This review highlights the molecular mechanisms, clinical benefits and side effects of the most commonly used hormones in clinical treatment of wounds.

The development of hair follicles and nail

The hair follicle and nail unit develop and regenerate through epithelial-mesenchymal interactions. Here, we review some of the key signals and molecular interactions that regulate mammalian hair follicle and nail formation during embryonic development and how these interactions are reutilized to promote their regeneration during adult homeostasis and in response to skin wounding. Finally, we highlight the role of some of these signals in mediating human hair follicle and nail conditions.

Deep skin fibroblast-mediated macrophage recruitment supports acute wound healing

Epithelial and immune cells have long been appreciated for their contribution to the early immune response after injury; however, much less is known about the role of mesenchymal cells. Using single nuclei RNA-sequencing, we defined changes in gene expression associated with inflammation at 1-day post-wounding (dpw) in mouse skin. Compared to keratinocytes and myeloid cells, we detected enriched expression of pro-inflammatory genes in fibroblasts associated with deeper layers of the skin. In particular, SCA1+ fibroblasts were enriched for numerous chemokines, including CCL2, CCL7, and IL33 compared to SCA1- fibroblasts. Genetic deletion of Ccl2 in fibroblasts resulted in fewer wound bed macrophages and monocytes during injury-induced inflammation with reduced revascularization and re-epithelialization during the proliferation phase of healing. These findings highlight the important contribution of deep skin fibroblast-derived factors to injury-induced inflammation and the impact of immune cell dysregulation on subsequent tissue repair.

Modulating embryonic signaling pathways paves the way for regeneration in wound healing

Epithelial tissues, including the skin, are highly proliferative tissues with the capability to constant renewal and regeneration, a feature that is essential for survival as the skin forms a protective barrier against external insults and water loss. In adult mammalian skin, every injury will lead to a scar. The scar tissue that is produced to seal the wound efficiently is usually rigid and lacks elasticity and the skin's original resilience to external impacts, but also secondary appendages such as hair follicles and sebaceous glands. While it was long thought that hair follicles develop solely during embryogenesis, it is becoming increasingly clear that hair follicles can also regenerate within a wound. The ability of the skin to induce hair neogenesis following injury however declines with age. As fetal and neonatal skin have the remarkable capacity to heal without scarring, the recapitulation of a neonatal state has been a primary target of recent regenerative research. In this review we highlight how modulating dermal signaling or the abundance of specific fibroblast subsets could be utilized to induce de novo hair follicles within the wound bed, and thus to shift wound repair with a scar to scarless regeneration.

Identifying characteristics of dermal fibroblasts in skin homeostasis and disease

Heterogeneous dermal fibroblasts are the main components that constitute the dermis. Distinct fibroblast subgroups show specific characteristics and functional plasticity that determine dermal structure during skin development and wound healing. Although researchers have described the roles of fibroblast subsets, this is not completely understood. We review recent evidence supporting understanding about the heterogeneity of fibroblasts. We summarize the origins and the identified profiles of fibroblast subpopulations. The characteristics of fibroblast subpopulations in both healthy and diseased states are highlighted, and the potential of subpopulations to be involved in wound healing in different ways was discussed. Additionally, we review the plasticity of subpopulations and the underlying signalling mechanisms. This review may provide greater insights into potential novel therapeutic targets and tissue regeneration strategies for the future.

Inhibition of CK2α accelerates skin wound healing by promoting endothelial cell proliferation through the Hedgehog signaling pathway

Diabetes is a chronic disease characterized by perturbed glucose and lipid metabolism, resulting in high blood glucose levels. Many complications induced by endothelial dysfunction can cause disability and even death of diabetic patients. Here, we found that the protein level of casein kinase 2α (CK2α) was increased in the endothelium of mice with type I diabetes (T1D) induced by streptozotocin (STZ) injection. Although a potential correlation between the protein level of CK2α and endothelial dysfunction in diabetes was established, the contribution of CK2α to the progression of endothelial dysfunction in diabetes remained largely unknown. By using CX4945 (a selective CK2α antagonist) and Si-csnk2a1 (small interfering RNA targeting CK2α), we found that inhibition of CK2α accelerated skin wound healing in T1D mice by promoting proliferation of endothelial cells. Administration of CX4945 or Si-csnk2a1 rescued the impaired Hedgehog signaling pathway in high glucose-treated human umbilical vein endothelial cells (HUVECs). Exploration of the underlying molecular mechanism revealed that the protective effect of CK2α inhibition on angiogenesis, which contributes to skin wound healing in diabetic mice, was blocked by administration of GANT61 (an inhibitor targeting the Hedgehog signaling pathway). Our findings establish CK2α as a regulator of endothelial dysfunction in diabetes and demonstrate that inhibition of CK2α accelerates skin wound healing in T1D mice by promoting endothelial cell proliferation via the Hedgehog signaling pathway.

Skin fibroblast functional heterogeneity in health and disease

Fibroblasts are the major cell population of connective tissue, including the skin dermis, and are best known for their function in depositing and remodelling the extracellular matrix. Besides their role in extracellular matrix homeostasis, fibroblasts have emerged as key players in many biological processes ranging from tissue immunity and wound healing to hair follicle development. Recent advances in single-cell RNA-sequencing technologies have revealed an astonishing transcriptional fibroblast heterogeneity in the skin and other organs. A key challenge in the field is to understand the functional relevance and significance of the identified new cell clusters in health and disease. Here, we discuss the functionally distinct fibroblast subtypes identified in skin homeostasis and repair and how they evolve in fibrotic disease conditions, in particular keloid scars and cancer. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The origins of skin diversity: lessons from dermal fibroblasts

Skin is largely composed of an epidermis that overlies a supporting dermis. Recent advancements in our understanding of how diverse groups of dermal fibroblasts regulate epidermal and hair follicle growth and differentiation have been fueled by tools capable of resolving molecular heterogeneity at a single-cell level. Fibroblast heterogeneity can be traced back to their developmental origin before their segregation into spatially distinct fibroblast subtypes. The mechanisms that drive this lineage diversification during development are being unraveled, with studies showing that both large- and small-scale positional signals play important roles during dermal development. Here, we first delineate what is known about the origins of the dermis and the central role of Wnt/β-catenin signaling in its specification across anatomical locations. We then discuss how one of the first morphologically recognizable fibroblast subtypes, the hair follicle dermal condensate lineage, emerges. Leveraging the natural variation of skin and its appendages between species and between different anatomical locations, these collective studies have identified shared and divergent factors that contribute to the extraordinary diversity of skin.

The potential role of fibroblast-derived multi-peptide factors in activation of growth factors and β-Catenin in hair follicle cells

BACKGROUND

Dermal fibroblasts play a pivotal role in hair follicle regeneration during wound repair. Recently, dermal fibroblast-conditioned medium (DFCM), which contains multi-peptide factors (MPFs), has been used to promote wound repair.

AIM

This study aimed to investigate the stimulatory effects of MPF-containing DFCM on hair growth.

METHODS

MPF-containing DFCM was prepared using human neonatal dermal fibroblasts. Outer root sheath (ORS) and dermal papilla (DP) cells were cultured in MPF-containing DFCM. We examined the expression and secretion of growth factors and cytokines using quantitative polymerase chain reaction and a growth factor array. In addition, the effect of MPFs on β-catenin activity was determined using the TOPflash assay. All experiments were repeated at least three times with separate batches of cells.

RESULTS

MPF-containing DFCM increased keratinocyte growth factor (KGF), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF) mRNA expression in ORS cells and KGF and VEGF mRNA expression in DP cells. When ORS cells were treated with MPF-containing DFCM, the secretion of several growth factors, including EGF, VEGF, insulin-like growth factor-binding protein (IGFBP)-4, IGFBP-6, and fibroblast growth factor-7, was increased in the cell-cultured medium compared with that in control. Additionally, MPF-containing DFCM increased the transcriptional activation of β-catenin in DP cells.

CONCLUSIONS

These results suggest that MPF-containing DFCM might stimulate hair growth by inducing growth factors in ORS and DP cells and regulating β-catenin in DP cells.

Integrated analysis of miRNAs and mRNA profiling reveals the potential roles of miRNAs in sheep hair follicle development

BACKGROUND

Merino sheep exhibit high wool production and excellent wool quality. The fleece of Merino sheep is predominantly composed of wool fibers grown from hair follicles (HFs). The HF is a complex biological system involved in a dynamic process governed by gene regulation, and gene expression is regulated by microRNAs (miRNAs). miRNA inhibits posttranscriptional gene expression by specifically binding to target messenger RNA (mRNA) and plays an important role in regulating gene expression, the cell cycle and biological development sequences. The purpose of this study was to examine mRNA and miRNA binding to identify key miRNAs and target genes related to HF development. This will provide new and important insights into fundamental mechanisms that regulate cellular activity and cell fate decisions within and outside of the skin.

RESULTS

We analyzed miRNA data in skin tissues collected from 18 Merino sheep on four embryonic days (E65, E85, E105 and E135) and two postnatal days (D7 and D30) and identified 87 differentially expressed miRNAs (DE-miRNAs). These six stages were further divided into two longer developmental stages based on heatmap cluster analysis, and the results showed that DE-mRNAs in Stage A were closely related to HF morphogenesis. A coanalysis of Stage A DE-mRNAs and DE-miRNAs revealed that 9 DE-miRNAs and 17 DE-mRNAs presented targeting relationships in Stage A. We found that miR-23b and miR-133 could target and regulate ACVR1B and WNT10A. In dermal fibroblasts, the overexpression of miR-133 significantly reduced the mRNA and protein expression levels of ACVR1B. The overexpression of miR-23b significantly reduced the mRNA and protein expression levels of WNT10A.

CONCLUSION

This study provides a new reference for understanding the molecular basis of HF development and lays a foundation for further improving sheep HF breeding. miRNAs and target genes related to hair follicular development were found, which provided a theoretical basis for molecular breeding for the culture of fine-wool sheep.

GC-TOF/MS-Based Metabolomics for Comparison of Volar and Non-Volar Skin Types

Skin has heterogenous identities on different body sites despite similar cellular compositions. There are two types of skin, volar (palmoplantar) and non-volar (dorsal), which are characterized by epidermal thickness, pigmentation, and presence of hair follicles. However, the mechanisms underlying the development of these different skin types remain unclear. To investigate these, we profiled the cellular metabolites of volar and non-volar skin in mice using gas chromatography-time-of-flight/mass spectrometry (GC-TOF/MS), and further assessed the metabolic differences between them. In total, 96 metabolites from both volar and non-volar skin of mice were identified using the BinBase database system. Metabolomics analysis revealed important differences associated with amino acid metabolism (phenylalanine, tyrosine, and tryptophan biosynthesis; aspartate and glutamate metabolism), sugar metabolism (pentose phosphate pathway), and nucleotide metabolism (pyrimidine metabolism) in volar skin. Fifty metabolites were identified as potential biomarkers differentiating the physiological characteristics of these skin types. Of these, nine were highly increased whereas 41 were significantly decreased in volar skin compared with those in non-volar skin. Overall, these results provide valuable information for understanding the metabolic differences between volar and non-volar skin.

Dermal Hedgehog Signaling in Papillary Fibroblasts: An Emerging Key Player in Skin Regeneration

Wound repair involves the coordination of multiple skin cells and signaling pathways, and it results in tissue regeneration or scarring. In their article in the Journal of Investigative Dermatology, Frech et al., (2021) explore how Hedgehog (Hh) signaling influences the function of fibroblasts residing in the papillary and reticular dermis during wound healing. Their results reveal a pivotal role for Hh signaling in papillary fibroblasts related to hair follicle regeneration, which could open new therapeutic opportunities.